Visual query builder

Still working on:

* Docstrings/better variable names
* Precompute compatibility
* Adding a setting to disable pycode altogether
Currently $scope.args is just a list for the function args (for example `min`, `max` for rand_int). Currently the formats for inputs are poorly defined. I have been planning out a better UI (including not making the user type in 'day' for date trunc, etc) that has an input validation system, but I think it will have to go in the next PR if that is okay?